This invention relates to a fluid coupling and more particularly to a viscous fluid coupling for connecting the engine of an automotive vehicle to a cooling fan for the engine radiator.
Viscous couplings have been used for many years to provide the driving connection between an engine and its radiator fan to control the air flow through the cooling radiator. These couplings conventionally use a fluid medium, such as silicone oil, to transmit torque between rotatable coupling members.
Engine cooling studies on passenger cars and trucks have shown that operation of the fan for engine cooling purposes is required only a fraction of the time, such as one-fifth, for example, the vehicle is on the road. Moreover, if the fan is run at a high speed, fuel may be wasted and the noise produced may be objectionable. Accordingly, the viscous couplings developed over the past several years sought to reduce the high speed operation of the fans as well as control the operation in an effort to reduce the total energy required for operating the fan. These viscous couplings relied on the drive force created by fluid shear which occurred between the two members having mating annular grooves and ridges or mating surfaces. The fan speed was dependent upon the speed of the driving element and the amount of working fluid in the mating grooves and ridges or between the operating surfaces. When the grooves were only partially filled, considerable slip occurred between the two members and the fan speed would be considerably less than the speed of the driving member. If the space between the grooves and ridges were completely filled with fluid, the slip would, below a predetermined speed, such as 2000 rpm, be reduced. When the speed of the driving element rose above a predetermined amount, the viscosity and shear characteristics were such that an increased amount of slippage occurred to prevent substantial increase in fan speed.
The amount of fluid in the shear area was controlled by a thermostatically activated reed valve which opened and closed a pumping hole in the apparatus. At low ambient temperatures, the pumping hole was fully open and the fluid would be pumped into a reservoir at a high rate, thus minimizing the fluid in the shear space. At higher ambient temperatures, the reed valve would close the pumping hole to prevent the fluid from being pumped into the reservoir and the amount of fluid in the shear space would increase, resulting in higher shear forces and reduced slip between the members.
These viscous couplings often require a number of precision machining operations during the manufacture thereof. In addition, relatively expensive shaft seals and bearings are often utilized. The present invention relates to an improved viscous coupling of the general type described for connecting a fan to an automotive vehicle engine.